KR20090040891A - Flat-fold respirator with monocomponent filtration/stiffening monolayer - Google Patents

Abstract

A flat-fold respirator is made from a stiff filtration panel joined to the remainder of the respirator through at least one line of demarcation. The panel contains a porous monocomponent monolayer nonwoven web that contains charged intermingled continuous monocomponent polymeric fibers of the same polymeric composition and that has sufficient basis weight or inter-fiber bonding so that the web exhibits a Gurley Stiffness greater than 200 mg and the respirator exhibits less than 20 mm H2O pressure drop. The respirator may be formed without requiring additional stiffening layers, bicomponent fibers, or other reinforcement and can be flat-folded for storage. Scrap from the manufacturing process may be recycled to make additional stiff filtration panel web.

Description

FLAT-FOLD RESPIRATOR WITH MONOCOMPONENT FILTRATION / STIFFENING MONOLAYER}

The present invention relates to a flat-fold respirator worn by a person to prevent them from inhaling airborne contaminants.

Personal respirators are commonly used to prevent the wearer from inhaling particles suspended in the air or breathing unpleasant or harmful gases. Respirators are generally of one of two types: molded cup form or flat fold form. The flat fold form has the advantage of being able to carry in the pocket of the wearer until needed, unfoldable for use and refolded flat for storage. Commercially available flat fold respirators typically include reinforcing members (e.g., elastic support structures or other support elements, such as US Pat. No. 4,300,549 to Parker) or reinforcing layers (e.g., polyester fibers). High basis weight nonwoven webs, including large diameter high modulus fibers, such as US Pat. No. 6,123,077 to Bostock et al., Are used to impart greater structural stability to the unfolded respirator. The reinforcing member or reinforcing layer may help prevent bending of the respirator during the breathing cycle, thereby inhibiting or preventing the wearer's lips and nostrils from contacting the inner surface of the respirator.

Reinforcing members and reinforcing layers are beneficial in that they improve the structural integrity of the respirator, but the use of such components can undesirably increase the weight, volume and cost of the entire respirator. Because the reinforcing members and reinforcing layers do not provide significant filtration performance and limit the extent to which unmanufactured scrap can be recycled, we have sought to remove these components from the flat fold respirator. Some patents mention that the reinforcing member or reinforcing layer is merely optional or preferred (see, for example, US Pat. No. 6,123,077 and Hubbard et al. US Pat. No. 4,920,960). Since the removal of these components undesirably weakens when the respirator is worn out, it is actually difficult to remove these components.

1 is a side view of a flat fold respirator 10 according to the present invention.

FIG. 2 is a front view of the flat fold respirator 10 of FIG. 1, shown in an open-to-use configuration.

3 is a schematic diagram of an exemplary manufacturing process for producing a flat fold respirator in accordance with the present invention.

4 is a schematic diagram of a preform 146 manufactured using the process of FIG. 3 in accordance with the present invention.

5 is a front view of another embodiment of a flat fold respirator 160 in accordance with the present invention in a flat folded shape.

FIG. 6 is a front view of the flat fold respirator 160 of FIG. 5 in accordance with the present invention in an open ready shape.

FIG. 7 illustrates a rigid monocomponent single layer web 264 in accordance with the present invention, using a meltblowing die 202 in which orifices 246 and 248 flow at different rates or are fed polymers of the same polymer composition having different viscosities. A schematic cross sectional view of an exemplary process for making.

8 is an exit end view of an exemplary meltblowing die for use in the process of FIG. 7.

9 is a schematic cross-sectional view of an exemplary process for producing rigid monocomponent single layer web 320 in accordance with the present invention using a meltblowing die having a plurality of larger orifices and smaller orifices.

10 is a perspective view of the exit end of an exemplary meltblowing die for use in the process of FIG. 9.

FIG. 11 is a schematic side view of an exemplary process for producing rigid one-component monolayer webs using meltspinning and quench forced flow heaters.

12 is a perspective view of the heat treatment portion of the apparatus shown in FIG. 11.

FIG. 13 is a schematic enlarged view of the apparatus of FIG. 12.

Like reference symbols in the various drawings of the accompanying drawings indicate like elements. Elements in the figures are not drawn to scale.

Applicants have now discovered a way to provide both reinforcement and filtration performance in a single layer so that a flat fold respirator with reduced one or more of weight, volume and manufacturing cost can be produced.

In one aspect, the present invention provides a flat fold type personal respirator comprising at least one rigid filtration panel coupled to the remainder of the respirator via at least one line of demarcation, the panel comprising: A porous one-component monolayer nonwoven web, the web comprising charged and mixed continuous one-component polymer fibers of the same polymer composition, the web exhibiting a Gurley Stiffness of greater than 200 mg and a respirator of 0.19 kPa (20 It has sufficient basis weight or interfiber bonds to exhibit a pressure drop less than mm H ₂ O). The respirator may be folded into a substantially flat folded shape and unfolded into a convexly open shape.

In another aspect, the present invention provides a method of making a flat fold personal breathing apparatus, the method

a) obtaining a monocomponent monolayer nonwoven web comprising charged and mixed continuous monocomponent polymer fibers of the same polymer composition and having sufficient basis weight or interfiber bonds to exhibit a Gurley stiffness of greater than 200 mg;

b) forming at least one divider in the charged web to provide at least one panel at least partially defined by the divider; And

c) configuring the web to provide a mask body that exhibits a pressure drop less than 20 mm H ₂ O and that can be folded into a substantially flat folded shape and unfolded into a convexly open shape.

In another aspect, the invention provides a method of making a flat fold personal respirator, the method

a) forming a monocomponent monolayer nonwoven web of mixed continuous monocomponent polymer fibers of the same polymer composition and charging the web, wherein the web has a sufficient basis weight or interfiber bond to exhibit a Gurley stiffness of greater than 200 mg Has-;

b) forming at least one divider in the charged web to provide at least one panel at least partially defined by the divider; And

c) configuring the web to provide a mask body that exhibits a pressure drop less than 20 mm H ₂ O and that can be folded into a substantially flat folded shape and unfolded into a convexly open shape.

Product complexity and waste can be reduced by removing a separate reinforcement layer and potentially removing another layer, such as an outer cover web layer. Also, if both the reinforcing layer fibers in the respirator and the fibers of any other layer (eg, the inner or outer cover web layer) have the same polymer composition and no external bonding material is used, the unused scrap may require additional starting material. It can be recovered to make and fully recycled.

These and other aspects of the invention will be apparent from the detailed description below. In any case, however, the above summary should not be interpreted as a limitation on the subject matter of the invention, which is limited only by the appended claims, which may be amended during the filing process.

As used herein, the terms provided below will have the following meanings.

"Attenuating the filaments into fibers" means the conversion of a segment of a filament into a larger length and smaller size segment.

By "bimodal mass fraction / fiber size mixture" is meant a collection of fibers having a histogram of mass fractions versus fiber size in microns indicating at least two modes. The bimodal mass fraction / fiber size mixture may comprise more than two modes, for example it may be a mass fraction / fiber size mixture of the trimodal mode or more modes.

The term "bimodal mass count / fiber size mixture" means the number of fibers (degrees) versus micrometers in which the corresponding fiber size represents at least two modes that differ by at least 50% of the smaller fiber size. Means an aggregate of fibers having a histogram of fiber size of. The dual mode fiber number / fiber size mixture may comprise more than two modes, for example it may be a fiber number / fiber size mixture in triple mode or higher mode.

"Bonding" means firmly bonding together when used for a fiber or a fiber assembly, wherein the bonded fibers are generally not separated when the web is subjected to normal handling.

“Grayed” is 20 grays of 1 mm beryllium-filtered 80 KVp X-rays when evaluated for percent dioctyl phthalate (% DOP) transmission at a cotton speed of 7 cm / sec when used for fiber aggregates. A fiber that exhibits a loss of at least 50% of the quality factor (QF) (described below) after exposure to absorbed dose.

By “continuous” is meant a fiber having an essentially infinite aspect ratio (ie, a ratio of length to size of at least about 10,000 or more) when used with respect to a fiber or fiber assembly.

“Effective Fiber Diameter (EFD)” is used in any cross-sectional fiber web that is circular or non-circular when used for fiber assemblies [Davies, CN, "The Separation of Airborne Dust and Particles", Institution means a value determined according to the method described in of Mechanical Engineers, London, Proceedings 1B, 1952.

"Filtration panel" means a portion of a fold-flat respirator that has sufficient filtration capability to remove one or more airborne particulate contaminants and that has one or more identifiable boundaries when the respirator is deployed for use.

A “flat-fold respirator” can be folded flat for storage and unfolded to at least one's nose and mouth to be worn to remove one or more airborne contaminants when worn by such a person. Means the apparatus

"Line of demarcation" means a fold, seam, weld, joint or other visible feature that provides an identifiable boundary and optionally a hinge area for the respiratory filtration panel.

"Meltblown" when used for a nonwoven web, extrudes a fiber forming material through a plurality of orifices to form a filament, while simultaneously filamenting the filaments with air or other entraining fluid to make the filaments into fibers By web, it is then formed by collecting a layer of elongated fibers.

"Meltblown fibers" means fibers produced by extruding a molten fiber forming material through an orifice in a die into a high velocity gas stream, wherein the extruded material is first elongated and then solidified as an aggregate of fibers do. Meltblown fibers are generally not oriented. Although meltblown fibers have been reported to be discontinuous at times, the fibers are usually large enough to remove one complete meltblown fiber from such a collection of fibers or to normally track one meltblown fiber from start to finish. It is long and entangled.

“Meltspun”, when used for nonwoven webs, extrudes a low viscosity melt through a plurality of orifices to form filaments, and the filaments are quenched with air or other fluid to solidify at least the surface of the filaments, at least A web formed by contacting partially solidified filaments with air or other fluid to elongate the filaments into fibers and collecting layers of the elongated fibers.

By “meltspun fibers” is meant a fiber that exits the die and travels through a processing station that permanently draws the fiber and permanently orients the polymer molecules in the fiber to align with the longitudinal axis of the fiber. Such fibers are inherently continuous and entangled enough so that it is not usually possible to remove one complete meltspun fiber from such a collection of fibers.

“Microfibers” means fibers having a medium size (measured using a microscope) of 10 μm or less, and “ultrafine microfibers” are microfibers having a medium size of 2 μm or less “Submicron microfibers” means microfibers having a median size of 1 μm or less. When referring to batches, groups, arrays, and the like of certain types of microfibers herein, such as “arrays of submicrometer microfibers,” this refers to arrays or batches of submicrometer dimensions. It is not meant to be such a part, but means a complete population of micro fibers in such an array or a complete population of a single batch of micro fibers.

A "mode" is used for histograms of mass fractions versus fiber size in micrometers or histograms of fiber counts in fiber number (degrees) versus micrometers and their heights are 1 and 2 μm smaller than local peaks and 1 and 2 Micron means a local peak larger than the height for a larger fiber size.

"Monocomponent" means a fiber having essentially the same composition across its cross-section when used for a fiber or a fiber assembly, wherein a one-component means that a continuous phase of uniform composition crosses and crosses the cross-section of the fiber Blends that extend over (ie, polymer alloys) or additive containing materials.

A “monolayer”, when used for a nonwoven web, has a generally uniform distribution of similar fibers throughout the cross section of the web (in addition to the fiber size) and exists throughout the cross section of the web (relative to the fiber size). Means having fibers representing the population of each mode. Such monolayer webs may have a generally uniform fiber size distribution throughout the cross section of the web, or for example the preponderance of larger size fibers proximate one major face of the web and the other major face of the web. It may have a depth gradient of fiber size, such as the preponderance of smaller size fibers close to.

“Nominal Melting Point” is the peak of a secondary heating, total-heat-flow differential scanning calorimetry (DSC) plot within the melting region of the polymer, if there is only one maximum in that region. Means maximum; If there is more than one maximum that indicates more than one melting point (eg, due to the presence of two distinct crystal phases), it means the temperature at which the highest amplitude melting peak occurs.

"Nonwoven web" means a fibrous web characterized by entanglement or point bonding of the fibers.

"Of the same polymeric composition" has essentially the same repeating molecular units, but may differ in molecular weight, melt index, manufacturing method, commercial form, etc., optionally in small amounts (e.g., A polymer that may contain less than about 3 weight percent of electret charging additive.

When used for polymer fibers or aggregates of such fibers, "oriented" means that at least some of the polymer molecules of the fiber are aligned in the length direction of the fiber as a result of the fiber passing through equipment such as an elongation chamber or mechanical drawing machine. It means to be. The presence of orientation in the fiber can be detected by various methods, including birefringence measurement and wide angle x-ray diffraction.

"Porous" means air permeability.

"Separately prepared smaller size fibers" means that a stream of smaller sized fibers is initially produced from a stream of larger sized fibers (eg, over a distance of at least about 25 mm (1 inch)). Refers to a stream of smaller sized fibers produced from a fiber forming apparatus (eg, a die) that is spatially separated at, but positioned to merge in the air and disperse into a stream of larger sized fibers.

“Self-supporting” when used for nonwoven webs or panels, includes a wire, mesh or other that has a composition that differs from that of the web panel and provides increased rigidity to one or more portions of the web or panel. It does not include an adjacent reinforcing layer of reinforcing material.

"Size" means the fiber diameter in the case of a fiber having a circular cross section when used for a fiber, or the length of the longest chord on the cross section that can be constructed across a fiber having a non-circular cross section. .

In the practice of the present invention, various flat fold-type personal respirators can be made using the rigid filtration panels described herein. One such flat fold respirator is shown in FIG. 1 illustrating a respirator 10 having first and second dividing lines A and B. 2 shows a front view of the instrument 10 in a flared ready-to-use configuration. The instrument 10 includes a body 12 comprising six filtration panels. Three of these panels are shown in FIG. 1 as the right top panel 14, right center panel 16 and right bottom panel 18 (the terms left, right, top and bottom are used from the perspective of the wearer). . The remaining three panels are shown in FIG. 2 as left top panel 20, left center panel 22 and left bottom panel 24. Vertical bisecting lines 26 divide the left and right halves of the instrument 10. Panels 14 and 20 are connected via weld seam 28. Panels 16 and 22 are connected via a central vertical fold 30. Panels 18 and 24 are connected via weld seam 32. The panels 14, 16 are connected in this embodiment via weld joints A extending over some, but not all, of the area between the panels 14, 16. In a similar manner, panels 16 and 18 are connected via weld seam B, panels 20 and 22 are connected through weld seam A ', and panels 22 and 24 are weld seam B. Is connected via '). One or more of the panels 14, 16, 18, 20, 22, 24 may be provided as separate components, at least one of the filtration panels 14, 16, 18, 20, 22, 24, more preferably Is a rigid filtration panel as at least two, most preferably all as described in more detail below. When each of the filtration panels 14, 16, 18, 20, 22, 24 is a rigid filtration panel, they are preferably formed of a single preform made from the disclosed one-component monolayer nonwoven web. The disclosed rigid filtration panels also provide both airborne contaminant filtration and respiratory enhancement properties in a single nonwoven layer, except for any inner or outer cover web layers that may be present. The instrument 10 may be folded in half (eg, in a package before use or for storage in a wearer's pocket) along the line 26 corresponding to the fold 30 in this embodiment. The face edge 34 is shaped to provide a suitable seal for the wearer's balls, chin and nose. The instrument 10 preferably also includes additional components such as a reinforcing nosepiece 36 and attachments such as earloops 38. Some wearers would prefer a mechanism that is attached via one or two headbands (not shown in FIGS. 1 and 2) instead of earrings 38. The shape and size of the instrument 10 can be conveniently changed by changing the shape or orientation of the seams 28, 32. The seams 28, 32 may be straight or curved as necessary, for example, to achieve a good fit to the wearer's face. The orientations of the seams 28, 32 are first angle 40 and second angle 42 drawn with respect to the fold 30 and the first origin 44 or the fold 30 and the second origin 46, respectively. ) May be conveniently defined. The first angle 40 can be, for example, about 110 degrees to about 175 degrees, or about 140 degrees to about 155 degrees. The second angle 42 can be, for example, about 100 degrees to about 165 degrees, or about 135 degrees to about 150 degrees. By varying the shape of the seams 28, 32, the first angle 40, or the second angle 42, the fit of the instrument 10 to the wearer's face can be easily changed to accommodate a variety of face sizes and shapes. Can be. Those skilled in the art will appreciate the size and seam 28, 32 of the welded, sewn or otherwise fastened instrument 10 by varying the angle of each of the first angle 40 and the second angle 42. It will be appreciated that the length can be changed accordingly. The seams 28, 32 may have a length of, for example, about 40 mm to about 80 mm, and do not necessarily have the same length. Further details regarding respirators such as instrument 10 and their manufacture, except for rigid filtration panels, can be found in US Pat. No. 6,394,090 B1 (Chen et al.).

FIG. 3 shows a schematic diagram of one production process 120 for producing a flat fold type breathing apparatus similar to that shown in FIGS. 1 and 2. Optional inner cover web 124 and rigid filtration layer 126 are preferably supplied in roll form for a substantially continuous process. To facilitate the recycling of unused scrap, the inner cover web 124 is preferably a one-component web of the same polymer composition as the rigid filtration layer 126. For example, the inner cover web 124 and the rigid filtration layer 126 can both be polypropylene webs. Rigid filtration layer 126 may optionally be covered by outer cover web 132. When used, outer cover web 132 is preferably a one-component web of the same polymer composition as inner cover web 124 and rigid filtration layer 126. Preferably, at least the final outer surface of the rigid filtration layer 126 (ie, the surface facing away from the wearer in the finished respirator) is calendered, which can sufficiently prevent shedding so that the outer cover web 132 ) Can be omitted. If both major surfaces of the rigid filtration layer 126 are sufficiently calendered, shedding can be sufficiently prevented so that both the inner cover web 124 and the outer cover web 132 may be omitted. .

The resulting one, two or three layer web assembly 134 may be held together by surface forces, electrostatic forces, thermal bonds, adhesives or other suitable means familiar to those skilled in the art. The web assembly 134 may then be welded and trimmed at the welding station 136 to form a partial preform 138. The preform 138 is preferably substantially flat, so that it can be formed at a relatively high speed and at a relatively low cost without requiring special manufacturing equipment, such as a shell mold, to which the desired respirator matches. The partial preform 138 then passes through a separation station 140 where at least one divider line is formed in the partial preform 138 to produce a separate preform 142. Desired dividers or dividers can be formed by a variety of techniques including ultrasonic welding, application of pressure (with or without heat), sewing, application of adhesive bars, and the like. The divided preform 142 shown in FIG. 3 includes four dividing lines, denoted as A, A ', B, and B'. Dividers or dividers can help prevent or inhibit delamination of layers in the preform, can increase the stiffness of one or more filtration panels during wear, and when the respirator is unfolded for use or folded for storage Flexibility can be improved at the boundary between the filtration panels. The separated preform 142 then forms a punched scrap portion 148 in which the finished preform 146 can be removed from the web assembly 134 and wound onto a take-up reel 150. The remainder may be advanced to cutting station 144. If the various layers in the scrap portion 148 are webs having the same polymer composition, the scrap portion 148 may be immediately or at any convenient subsequent step (eg, grinding apparatus, extruder or other regeneration familiar to those skilled in the art). Can be recovered and regenerated), which can be made from new starting materials. The starting materials can be used, for example, to make one or both of the cover web 124 and the rigid filtration layer 126, with respect to the amount of electret charging additive when used to make the filtration layer 126. Appropriate adjustments are made.

Referring now to FIG. 4, the preform 146 can then be folded along the bisectoral fold 18, followed by seams 28, 32 (FIG. 1 and FIG. 1) that will affect the final size of the instrument 10. Welding, sewing or otherwise fastening along lines C and D at predetermined angles 40 and 42 to form (shown in FIG. 2). The preform 142 may also be trimmed to remove the waste portions 152, 154 (eg, before, during, or after the seams 28, 32 are formed). If each of the various layers in the waste portions 152 and 154 have the same polymer composition, the waste portions 152 and 154 can be recycled and made of new starting materials as described above. Any other desired attachment may be attached and the finished respirator may be packaged in any convenient manner, including individual packaging and bulk packaging. Those skilled in the art will appreciate that attachments such as nose covers 36 may be attached more conveniently at other stages of the manufacturing process. For example, the nose cover may be preliminary on the outer or inner surface of either the inner cover web 124 or the rigid filtration layer 126 before the webs are joined or before the preform is cut from the waste portion 148. It may be placed on or within the preform 142 before or after the seams 28, 32 are formed or after the seams 28, 32 are formed.

Another flat fold respirator that may be formed from the disclosed rigid filtration panel is shown in FIGS. 5 and 6, which show the instrument 160 in a flat folded shape and in an unfolded ready-to-use configuration, respectively. The instrument 160 preferably includes a central panel 162 made from the disclosed rigid filtration web. The instrument 160 also includes an upper panel 164 and a lower panel 166, which may also be made from the disclosed rigid filtration web, but are preferably made from conventional ones other than the rigid filtration web. Panel 162 is coupled to panels 164 and 166 through seams 168 and 170, respectively. The panel 162 preferably has a substantially oval shape, and the seams 168 and 170 preferably provide a respirator with comfortable close wear features, including an off-the-face shape. Curved or curved. In the embodiment shown in FIGS. 5 and 6, each of the center panel 162, top panel 164, and bottom panel 166 is non-pleated. The instrument 160 may also include an attachment point 172, a headband 174, and a nose clip 176. Further details regarding respirators such as instrument 160 can be found in US Pat. No. 6,123,077 (Bostock et al.). Another exemplary embodiment of such a device comprises a central panel made from the disclosed rigid filtration web and having a width of about 160 to 220 mm and a height of about 30 to 110 mm, wherein the device is at least partially covered by an upper panel or a lower panel. It can be folded flat for storage in contact with the surface of the central panel and in contact with the lower panel or a portion of the upper panel.

Various other flat fold respirators can be formed from the disclosed rigid filtration webs. Examples of such respirators include US Pat. Nos. 2,007,867 (Le Duc), 2,265,529 (Kemp), 2,565,124 (Durborow), 2,634,724 (Burns), 2,752,916 (Haliczer), 3,664,335 (Boucher et al.), 3,736,928 (Andersson et al.), 3,971,369 (Aspelin et al.), 4,248,220 (eg White, 4,300,549 (Parker), 4,417,575 (Hilton, etc.), 4,419,993 (Peterson), 4,419,994 (Hilton), 4,600,002 (Mariya neck) Maryyanek et al.), 4,920,960 (Hubbard et al.), 5,322,061 (Brunson), 5,701,892 (Bledstein), 5,717,991 (Nozaki et al.) ), 5,724,964 (Brunson et al.), 5,735,270 (Bayer) and 6,474,336 B1 (Wolfe), and British Patent Application No. 2 103 491 (American Optical Corporation). Included).

The disclosed respirator may be pleated or wrinkled, and is preferably wrinkled. The disclosed respirators may also include one or more molded parts or panels, but are preferably made without the need for molding. The disclosed rigid filtration panel may correspond to a small, most or even all of the available respiratory filtration area. The disclosed folds, seams, welds, joints or other dividers can be straight, curved, or curved. In some embodiments that include multiple dividers, the divider or dividers can intersect other dividers or dividers. In other embodiments, no dividing line will intersect the other dividing line. The disclosed respirator can have a pressure drop of less than 20 mm H ₂ O when exposed to 1 wt% sodium chloride aerosol flowing at 95 L / min. For example, it may have a pressure drop less than 10 mm H ₂ O (0.09 kPa). The disclosed respirators may also have a maximum transmission of less than 20% when exposed to 1 wt% sodium chloride aerosol flowing at 95 L / min. For example, it may have a maximum loading penetration of less than 5% or a maximum loading transmission of less than 1% when exposed to 0.075 μm 2% sodium chloride aerosol flowing at 85 L / min.

Various polymeric fiber forming materials can be used to make the disclosed rigid filtration webs. The polymer may be essentially any semicrystalline thermoplastic fiber forming material capable of undergoing selected fiber and web forming processes and providing a charged nonwoven web that will maintain satisfactory electret properties or charge separation. Preferred polymeric fiber forming materials are nonconductive semicrystalline resins having a volume resistivity of at least 10 ¹⁴ ohm-cm at room temperature (22 ° C). Preferably, the volume resistivity is at least about 10 ¹⁶ ohm-cm. The resistance of the polymer fiber forming material can be measured according to the standardized test ASTM D 257-93. The polymeric fiber forming material also preferably is substantially free of components such as antistatic agents that can significantly increase electrical conductivity or otherwise interfere with the fiber's ability to receive and maintain electrostatic charges. Some examples of polymers that can be used in the chargeable web are polyolefins such as polyethylene, polypropylene, polybutylene, poly (4-methyl-1-pentene) and cyclic olefin copolymers, and thermoplastics containing combinations of such polymers. Polymers. Other polymers that may be used but may be difficult to charge or may quickly lose charge are polycarbonates, block copolymers such as styrene-butadiene-styrene and styrene-isoprene-styrene block copolymers, polyesters such as polyethylene tere Phthalates, polyamides, polyurethanes, and other polymers familiar to those skilled in the art. The disclosed rigid filtration webs are preferably made from poly-4-methyl-1 pentene or polypropylene. Most preferably, the web is made from polypropylene homopolymers, in particular because of their ability to retain charge in a moisture environment.

Additives may be added to the polymer to improve the performance of the filtration web, electret charging capacity, mechanical properties, aging properties, coloring, surface properties or other characteristics of interest. Representative additives include fillers, nucleating agents (e.g., MILLAD ™ 3988 dibenzylidene sorbitol, available from Milliken Chemical), electret charge promoting additives (e.g., tristearyl melamine, and Ciba Specialty). Various light stabilizers such as CHIMASSORB ™ 119 and Chimassorb 944 from Ciba Specialty Chemicals), curing initiators, reinforcing agents (eg poly (4-methyl-1-pentene)), surface activation Agents and surface treatment agents (e.g., fluorine atom treatment agents to improve filtration performance in oily mist environments as described in US Pat. Nos. 6,398,847 B1, 6,397,458 B1, and 6,409,806 B1 to Jones et al.). Include. The type and amount of such additives will be familiar to those skilled in the art. For example, the electret charge promoting additive is generally present in an amount of less than about 5 weight percent, more typically less than about 2 weight percent.

The disclosed rigid filtration webs may have a variety of effective fiber diameter (EFD) values, for example about 5 to about 40 μm, or about 6 to about 35 μm. The web may also have various basis weights, eg, about 100 to about 500 g / m 2 (gsm) or about 150 to about 250 gsm. The disclosed webs can have Gurley stiffness values of at least about 200 mg, at least about 300 mg, at least about 400 mg, at least about 500 mg, at least about 1000 mg or at least about 2000 mg.

The disclosed rigid filtration webs are disclosed in US Patent Applications Nos. 11 / 461,136 and 11 / 461,145, filed July 31, 2006, and US Patent Application No. 11 / 693,017, filed March 29, 2007. As the web described in, it may conveniently be formed as a web comprising a bimodal mass fraction / fiber size mixture of microfibers and larger size fibers. The manufacturing process described in the latter application is exemplary and can be summarized as follows. 7 and 8 illustrate an apparatus 200 for making a porous monocomponent nonwoven web comprising a bimodal fiber number / fiber size mixture of mixed continuous microfibers and larger size fibers of the same polymer composition. do. The meltblowing die 202 is supplied with a liquefied first fiber forming material supplied from the hopper 204, the extruder 206 and the conduit 208 at a first flow rate or first viscosity. Die 202 is separately fed with a liquefied second fiber forming material of the same polymer composition supplied from hopper 212, extruder 214 and conduit 216 at a different second flow rate or viscosity. Conduits 208, 216 may include first and second die cavities 218, 220 positioned within generally symmetrical first and second portions 222, 224 forming an outer wall for die cavities 218, 220. Each is in fluid communication. The generally symmetric first and second portions 226, 228 form an inner wall for the die cavities 218, 220 and meet at the seam 230. Portions 226 and 228 may be separated along most of the length by insulator 232. Deflector plates 240, 242, deflector plates guide the stream of elongation fluid (eg, heated air) so that they converge on an array of filaments 252 emerging from the meltblowing die 202 and filaments 252. ) Into fibers 254. Fiber 254 lays against porous collector 256 and forms freestanding nonwoven meltblown web 258. Web 258 may optionally be calendared using, for example, rollers 260 and 262 to provide calendared web 264. The rate at which the polymer is fed from the hoppers 204, 212, the rate at which the collector 256 is operated, or the temperature used when the device 200 is operating, can be adjusted to provide a collected web with the desired degree of Gurley stiffness. .

8 shows, in an outlet end perspective view, the meltblowing die 202 with the exaggerated gas deflector plates 240, 242 removed. Portions 222 and 224 meet along seam 244 where a first set of orifices 246 and a second set of orifices 248 are positioned and through which an array of filaments 252 emerge. The die cavities 218, 220 are in fluid communication with the first set of orifices 246 and the second set of orifices 248 through passages 234, 236, 238, respectively.

The apparatus shown in FIGS. 7 and 8 provides a stream of larger size fibers coming out of one die cavity and smaller size fibers coming out of another die cavity, thereby mixing mixed larger size fibers of the same polymer composition. And in various modes or in various ways to form a nonwoven web comprising a bimodal mass fraction / fiber size mixture of smaller size fibers. For example, a die cavity (208) through a larger size conduit 208 from each extruder 206, 214 (or, if necessary, from a single extruder with two outlets not shown in FIG. 7). 218 and through the smaller sized conduit 216 to the die cavity 220 to produce smaller sized fibers from orifice 246 and larger sized fibers from orifice 248. . The same polymer can be fed from the extruder 206 into the die cavity 218 and from the extruder 214 into the die cavity 220 with the extruder 206 having a larger diameter or higher operating temperature than the extruder 214. Can be fed to die cavity 218 at higher flow rate or lower viscosity and to die cavity 220 at lower flow rate or higher viscosity to draw smaller sized fibers from orifice 246 and Larger sized fibers may be produced from orifice 248. Die cavity 218 may be operated at high temperature and die cavity 220 may be operated at low temperature, producing smaller sized fibers from orifice 246 and larger sized fibers from orifice 248. can do. Low melt index versions within the extruder 206 such that polymers of the same polymer composition but different melt indexes (eg, produce smaller sized fibers from orifice 246 and larger sized fibers from orifice 248). And a polymer of a high melt index in the extruder 214 can be fed from the extruder 206 to the die cavity 218 and from the extruder 214 to the die cavity 220. Those skilled in the art will appreciate incorporating solvent in other techniques (eg, streams of liquefied fiber forming material flowing into die cavity 218, or shorter flow paths through die cavity 218 and die cavity 220). It will be appreciated that a longer flow path through)) and combinations of such techniques with the various modes of operation described above may also be used.

In the embodiment shown in FIG. 8, the orifices 246, 248 are arranged in a single row alternating order over the outlet end of the die 202, each in a 1: 1 ratio with the die cavities 218, 220. Communicate. Other arrangements of orifices and other ratios of the number of orifices 246 and 248 may be used to provide nonwoven webs with altered fiber size distribution. For example, the orifices may be arranged in a plurality of rows (eg, 2, 3, 4 or more rows) between the elongated air outlets. If desired, patterns other than rows may be used, for example randomly placed orifices. When arranged in a plurality of rows, each row may include orifices from only one set or from both the first and second sets. The number of orifices in the first and second sets can vary in various ratios, for example 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90 And other ratios depending on the desired web structure. When orifices from both the first and second sets are arranged in one row or rows, the first and second sets of orifices need not be alternating, but instead in any desired manner, for example 1221, 1122211. 11112221111 and other arrangements according to the desired web structure. More than one set of orifices in fluid communication with the first, second, third, and additional die cavities in the meltblowing die, respectively, if necessary, to obtain a web having a fiber size distribution in triple or more modes. For example, first, second, third, and if desired additional sets of orifices.

The remainder of the relevant meltblowing device will be familiar to those skilled in the art. For example, further details regarding meltblowing can be found in Weente, Van A. "Superfine Thermoplastic Fibers", in Industrial Engineering Chemistry, Vol. 48, pages 1342 et seq. (1956)], or Report No. 4364 of the Naval Research Laboratories, published May 25, 1954, entitled "Manufacture of Superfine Organic Fibers" by Wente, V. A .; Boone, C. D .; and Fluharty, E. L., and US Pat. No. 5,993,943 (Bodaghi et al.).

The disclosed rigid filtration web may also be formed using apparatus 270 and meltblowing as shown in FIG. 9. The liquefied fiber forming polymer material supplied from the hopper 272 and the extruder 274 enters the meltblowing die 276 through the inlet 278, flows through the die cavity 280, and the die cavity 280 Exit the die cavity 280 through a row of larger sized orifices and smaller sized orifices (discussed below in connection with FIG. 10) arranged in a line across the front end of the fiber forming material. Extruded as an array of filaments 282. A set of interacting gas orifices, in which gas, typically heated air, is pressurized at a very high rate, elongates filament 282 into fibers 284. Fiber 284 is laid against porous collector 286 and forms a freestanding nonwoven meltblown web 288. The web may optionally be calendared using, for example, rollers 260 and 262 to provide a calendared web 289. The rate at which the polymer is fed from the hopper 272, the rate at which the collector 286 is operated, or the temperature used when the device 270 is operated, can be adjusted to provide a collected web with the desired degree of Gurley stiffness.

10 shows, in an outlet end perspective view, a meltblowing die 276 with the exaggerated gas deflector plate removed. Die 276 includes a protruding tip 290 having a larger orifice 294 and a row 292 of smaller orifices 296 forming a plurality of flow passages, the liquid liquefied through the flow passages. Forming material exits die 276 to form filament 282. Holes 298 receive through bolts (not shown in FIG. 10) that hold the various parts of the die together. In the embodiment shown in FIG. 10, the larger orifices 294 and the smaller orifices 296 have a 2: 1 size ratio and nine smaller orifices 296 for each larger orifice 294. There is. Other ratios of larger orifice sizes to smaller orifice sizes may be used, for example at least 1.5: 1, at least 2: 1, at least 2.5: 1, at least 3: 1, or at least 3.5: 1. Other ratios of the number of smaller orifices to larger orifices, for example 5: 1 or more, 6: 1 or more, 10: 1 or more, 12: 1 or more, 15: 1 or more, 20: 1 or more, or 30: 1 The above ratio may also be used. Typically, there will be a direct correspondence between the number of smaller orifices for larger orifices and the number of smaller diameter fibers (eg, microfibers under appropriate operating conditions) for larger sized fibers. As will be appreciated by those skilled in the art, suitable polymer flow rates, die operating temperatures, and elongation air flow rates are generated from elongated filaments formed by larger orifices with larger sized fibers and more microfibers. It is produced from elongated filaments formed by small orifices and should be selected so that the finished web has the desired structural, rigid and other physical properties.

The disclosed dual mode webs include using melt spinning to form larger size fibers and melt blowing to form separately produced smaller size fibers (eg, micro fibers) of the same polymer composition. Can be prepared in other ways. The larger sized fiber stream from the melt spinning die and the smaller sized fiber stream from the meltblowing die are made up of mixed larger and smaller fibers that can be merged in the air and then placed on a suitable collector. The combined stream may be provided to provide a nonwoven web comprising a bimodal mass fraction / fiber size mixture of larger and smaller size fibers. Further details regarding this process and nonwoven webs made as such are shown in US patent applications Ser. Nos. 11 / 457,906, 11 / 461,145 and 11 / 461,192, filed July 31, 2006. .

The disclosed rigid filtration webs also maintain orientation and fiber structure, similar to the webs described in US patent applications Ser. Nos. 11 / 457,899, 11 / 461,128, and 11 / 461,201, filed July 31, 2006. Monocomponent polymer fibers under thermal conditions sufficient to form a web of partially crystalline and partially amorphous oriented meltspun fibers of the same polymer composition bonded to form a cohesive and handleable web that can be further softened. It can conveniently be formed as a one-component monolayer nonwoven web of continuous one-component polymer fibers made by melt spinning, collecting, heating and quenching. The manufacturing processes described in these applications are exemplary and can be summarized as follows. The collected web of oriented semicrystalline meltspun fibers comprising an amorphous feature phase is: a) too short a time (preferably, heating) to melt the entire fiber (i.e. such fibers lose their individual fiber properties). The time is too short to cause significant warping of the fiber cross-section, forcing the fluid heated through the web to a temperature high enough to soften the amorphous characteristic phase of the fiber (approximately higher than the initial melting temperature of such fiber material) and and b) immediate quenching the web by forcing a fluid having a sufficient heat capacity through the web to solidify the softened fiber (ie, to solidify the amorphous feature phase of the softened fiber during heat treatment). Heating and quenching operations are performed. Preferably, the fluid passing through the web is a gas stream, preferably this fluid is air. In this context, "forcefully" passing a fluid or gas stream through a web means that in addition to normal room pressure, a certain force is applied to the fluid to propel the fluid through the web. In a preferred embodiment, the disclosed quenching step is concentrated and exits from the heater under pressure and contacts one side of the web, with the gas blowing device on the other side of the web to assist in aspirating the heated gas through the web. Passing the web on the conveyor through a device (which may be referred to as a quench flow heater, as described below) to provide a heated gas (typically air) stream, the generally heated stream being a (long slot or Knife- or curtain-like, as emanating from a rectangular slot, extending across the width of the web and uniform (i.e., having uniformity in terms of temperature and flow to heat the fibers in the web to a uniform degree of usefulness) . The heated stream is, in some respects, similar to a heated stream from a "through-air bonder" or "hot-air knife" but with special control to regulate the flow The heated gas can be distributed evenly and at a controlled rate through the width of the web to heat and soften the spun fibers to usefully high temperatures completely, uniformly and quickly. Forced quench immediately following heating to quickly freeze the fibers into a refined morphological shape (“immediately”) is part of the same operation, i. Means no intervening time). In a preferred embodiment, a gas apparatus is located downstream of the heated gas stream to draw a cooling gas or other fluid, such as ambient air, through the web immediately after the web is heated, thereby rapidly quenching the fibers. The heating length is such as by the length of the heating zone along the web travel path and by the speed at which the web is moved through the heating zone to the cooling zone to cause the intended melting / softening on the amorphous features without melting the entire fiber. Controlled.

Referring to FIG. 11, by introducing a polymer fiber forming material into the hopper 311, melting the material in the extruder 312, and pumping the melted material through the pump 313 into the extrusion head 310, The fiber forming material is moved to the extrusion head 310 within this exemplary apparatus. Solid polymeric materials in the form of pellets or other particulates are most commonly used and melt in a pumpable liquid state. The extrusion head 310 may be a conventional spinnerette or spin pack generally comprising a plurality of orifices arranged in a regular pattern, such as a straight row. A filament 315 of fiber forming liquid is extruded from the extrusion head and sent to a processing chamber or attenuator 316. The wash machine may be, for example, a movable wall wash machine such as shown in US Pat. No. 6,607,624 B2 (Berrigan et al.). As the conditions under which the filaments are exposed may vary, the distance 317 the extruded filaments 315 travel before reaching the elongator 316 may vary. An quench stream 318 of air or other gas may be provided to the extruded filaments to lower the temperature of the extruded filaments 315. Alternatively, a stream of air or other gas can be heated to facilitate drawing of the fibers. One or more streams of air or other fluid, such as the first air stream 318a blown transversely to the filament stream, which can remove unwanted gaseous material or smoke released during extrusion, and most desired temperature reduction. There may be a second quench air stream 318b that achieves. Even more quench streams may be used, for example, stream 318b itself may include more than one stream to achieve the desired level of quench. Depending on the process used or the type of finished product desired, the quench air may be sufficient to solidify the extruded filament 315 before it reaches the elongator 316. In other cases, the extruded filaments are still softened or molten until they enter the refiner. Alternatively, no quench stream is used, in which case any change in the extruded filament before the filament from which the ambient air or other fluid extruded between the extrusion head 310 and the refiner 316 enters the refiner It may be a medium for.

Filament 315 passes through slender 316 and is then discharged onto collector 319 where it is collected as a collection of fibers 320. Within the elongator, the filament is lengthened and reduced in diameter, the polymer molecules in the filament are oriented and at least some of the polymer molecules in the fiber are aligned with the longitudinal axis of the fiber. In the case of semicrystalline polymers, this orientation is usually sufficient to express strain induced crystallinity, which makes the resulting fiber very strong. Collector 319 is generally porous and a gas extraction device 414 can be positioned below the collector to assist in the lamination of the fibers onto the collector. The distance 321 between the muffler outlet and the collector can be varied to achieve a different effect. In addition, prior to collection, the extruded filaments or fibers may be subjected to a number of additional processing steps, such as additional drawing, spraying, and the like, not shown in FIG. After collection, the collected aggregate 320 is generally heated and quenched as described in more detail below, but the aggregate can be wound into a storage roll for later heating and quenching if desired. In general, when the assembly 320 is heated and quenched, it can be transferred to another device, such as optional calender rolls 322, 323, or rolled up to a storage roll 323 for later use. Can be.

In a preferred method of forming the web, the aggregate 320 of fibers is carried by a collector 319 to undergo heating and quenching operations as shown in FIGS. 12 and 13. For the sake of simplicity, in particular the apparatus shown in FIGS. 12 and 13 is often called a quench flow heater or more simply a quench heater. The collected aggregate 320 is first passed under a controlled heating device 400 mounted above the collector 319. Exemplary heating device 400 includes a housing 401 divided into an upper plenum 402 and a lower plenum 403. The upper and lower plenums are typically separated by a plate 404 perforated with a series of holes 405 of uniform size and spacing. Gas, typically air, is supplied from the conduit 407 through the opening 406 into the upper plenum 402, and the plate 404 is supplied with air into the upper plenum into the lower plenum 403. It acts as a flow distribution means that makes it evenly distributed when passed. Other useful flow distribution means include fins, baffles, manifolds, air dams, screens or sintered plates, ie devices for equalizing the distribution of air.

In the exemplary heating device 400, the bottom wall 408 of the lower plenum 403 is formed to have an elongate rectangular slot 409 through which the curtained stream of heated air from the lower plenum 410. Under this heating device 400 is blown onto the assembly 320 moving on the collector 319 (the assembly 320 and the collector 319 are shown partially cut away in FIG. 12). The gas blowing device 414 preferably extends long enough to lie under the slot 409 of the heating device 400 (as well as through the display area 420 beyond the heated stream 410, as described below). Extending downstream the web 418. Thus, the heated air in the plenum is under internal pressure in the plenum 403, and in slot 409 this air is also under the exhaust vacuum of the gas blowing device 414. To further control the evacuation force, a perforated plate 411 is positioned below the collector 319 to spread the stream of heated air 410 to the desired uniformity over the width or heating region of the collected assembly 320. It may impose some kind of back pressure or flow restriction means that contribute to the shaping and inhibit streaming through the possible low density portions of the collected aggregates. Other useful flow restriction means include screens or sintered plates.

The number, size, and density of openings in the plate 411 may vary within different regions to achieve the desired control. Large amounts of air pass through the fiber forming apparatus and must be discarded when the fiber reaches the collector within region 415. Sufficient air passes through the web and the collector in zone 416 to hold the web in place under various streams of process air. Sufficient opening is required within the plate under heat treatment region 417 and quench region 418 to allow the process air to pass through the web, and sufficient resistance is maintained to ensure that the air is distributed more evenly. The amount and temperature of heated air passing through the aggregate 320 is selected to lead to appropriate deformation of the shape of the fiber. In particular, the amount and temperature are chosen such that the fiber is heated to a) cause melting / softening of the significant molecular parts in the cross section of the fiber, such as the amorphous features of the fiber, but b) no complete melting of the other major phases, such as microcrystalline features. do. The term " melting / softening " is used because the amorphous polymer material is typically softened rather than melted, and the crystalline material that may be present to some extent in the amorphous feature is typically melted. This may also be described as heating to cause melting of a lower arrangement of microcrystals in the fiber, regardless of the phase. The fibers remain unmelted as a whole, for example the fibers generally retain the same fiber shape and dimensions as they had before treatment. Much of the phase on the microcrystalline features is understood to retain the existing crystal structure after heat treatment. The crystal structure may have been added to existing crystal structures, or in the case of highly arranged fibers, the crystal structure may have been removed to produce distinguishable amorphous and microcrystalline feature phases.

In order to achieve the intended fiber shape change throughout the collected aggregate 320, temperature-time conditions must be controlled over the entire heating zone of the aggregate. Desirable results have been obtained when the temperature of the stream of heated air 410 through the web is within the range of 5 ° C., preferably within 2 ° C. or even 1 ° C. across the width of the aggregate being treated (of heated air The temperature is often measured at the point of entry of the heated air into the housing 401 for easy control of operation, but may be measured adjacent to the web collected by the thermocouple). In addition, the heating device is operated to maintain a steady temperature in the stream over time, for example by quickly turning the heater on and off to avoid overheating or underheating.

In order to further control the heating and to complete the formation of the desired shape of the fibers of the collected aggregate 320, the aggregate is quenched immediately after the stream of heated air 410 is applied. Such quench can generally be obtained by drawing ambient air over the assembly 320 as the assembly leaves the controlled hot air stream 410. Reference numeral 420 in FIG. 13 denotes an area in which ambient air is sucked through the web by the gas extraction apparatus through the web. The gas extraction device 414 extends along the collector beyond the heating device 400 by a distance 418 to ensure complete cooling and quenching of the entire assembly 320 within the region 420. Air may be drawn under the base of the housing 401, for example in the region 420a indicated in FIG. 13, so that the air reaches the web immediately after the web leaves the hot air stream 410. The desired quench result is the rapid removal of heat from the webs and fibers, limiting the extent and nature of crystallization or molecular arrangements that will occur later in the fibers. Generally, the disclosed heating and quenching operations are performed when the web is moved through the operation on the conveyor, and the quenching is performed before the web is wound up to the storage roll at the end of the operation. The treatment time depends on the speed at which the web is moved through the operation, but in general the total heating and quenching operations are carried out in less than one minute, preferably less than 15 seconds. By rapid quenching from the molten / softened state to the solidified state, it is understood that the amorphous feature phase is frozen in more refined crystalline form with reduced molecular material that may interfere with softening or repeatable softening of the fibers. . Preferably, the aggregate is cooled by gas at a temperature at least 50 ° C. below the nominal melting point, and the quench gas or other fluid is preferably for a time of at least 1 second, preferably the time for which the heated stream contacts the web. Is applied for at least two or three times the time of. In any case, the quench gas or other fluid has sufficient heat capacity to rapidly solidify the fiber. Other fluids that may be used include water sprayed onto the fibers, such as heated water or steam to heat the fibers, and relatively cold water to quench the fibers.

Success in achieving the desired heat treatment and morphology on amorphous features can often be confirmed by DSC testing of representative fibers from the treated web, the treatment conditions being described in more detail in the aforementioned US patent application Ser. No. 11 / 457,899. It may be adjusted according to the information obtained from the DSC test as it is. Preferably, applying and quenching heated air is controlled to provide a web having properties that facilitate the formation of a suitable shaped matrix. If insufficient heating is used, the web can be difficult to mold. If excessive heating or insufficient quenching is used, the web may melt or become brittle and also may not take sufficient charge.

When dual mode rigid filtration webs are used, the microfibers may have a size range of, for example, about 0.1 to about 10 μm, about 0.1 to about 5 μm, or about 0.1 to about 1 μm. Larger size fibers may have a size range of, for example, about 10 to about 70 μm, about 10 to about 50 μm or about 15 to about 50 μm. Histograms of fiber fraction in mass fraction to micrometer units are, for example, microfiber modes of about 0.1 to about 10 micrometers, about 0.5 to about 8 micrometers or about 1 to about 5 micrometers, and greater than about 10 micrometers, about 10 to about 50 micrometers. It may have a larger size fiber mode of about 10 μm, about 10 to about 40 μm or about 12 to about 30 μm. The disclosed dual mode webs also exhibit at least two modes where the histogram of fiber number (degrees) versus fiber size in μm differs by at least 50%, at least 100%, or at least 200% of the smaller fiber size of the corresponding fiber size. It may also have a bimodal fiber number / fiber size mixture. The microfibers may also provide, for example, at least 20%, at least 40% or at least 60% of the fiber surface area of the web. When a web of partially crystalline and partially amorphous oriented meltspun fibers is used, the fibers are for example about 5 to about 70 μm, about 10 to about 50 μm or about 10 to about as measured using an optical microscope. It may have a size range of about 30 μm. Larger meltspun fibers generally produce a finished web that is more rigid.

Depending on the process and process conditions used to make the disclosed rigid filtration webs, some bonding may occur between the fibers during web formation, such that the finished web may comprise fibers bonded to each other at least at some fiber intersections. have. Further bonding between the fibers in the collected web may be necessary to provide a web with the desired degree of stiffness. However, excessive coupling may also need to be avoided to limit pressure drop or other completed web or respiratory properties.

After formation, the rigid filtration web is then subjected to charging and optional calendaring. Charging and calendering may be performed in any order, but it is preferred that charging is performed first to allow charge to be distributed over the entire web thickness. Charge can be imparted to the disclosed nonwoven web in a variety of ways. The charging was performed by contacting the web with water, for example, as disclosed in US Pat. No. 5,496,507 (Angadjivand et al., '507), as disclosed in US Pat. No. 4,588,537 (Klasse et al.). By corona treatment, for example by hydrocharging as disclosed in US Pat. No. 5,908,598 (Rousseau et al.), US Pat. No. 6,562,112 B2 (Jones et al.) And US Patent Application Publication No. 2003 / 0134515 A1 (David et al.) May be performed by plasma treatment, or a combination thereof.

Calendaring can be performed in a variety of ways familiar to those skilled in the art. Calendering is usually performed using heating and optional pressure (eg, to temperatures between the softening and melting points of the applicable polymer at applicable pressures), and point-bonding processes or smooth calender rolls. Roll calendaring is particularly useful and can be performed in a variety of ways. For example, the web may be passed one or more times between two mating heated metal rolls to provide a calendared web having two smooth sides. The web may also be passed one or more times between the heated metal roll and the mating elastic roll to provide a calendared web having one smooth face. The use of tighter roll gaps, higher nip pressures, higher temperatures or additional passages will generally increase the extent to which the web is strengthened. However, calendaring may undesirably increase the pressure drop or impair filtration performance in the finished respirator when performed to a very broad extent. Calendering will also typically make the calendered surface more dense and less porous. Calendaring one or both sides of the rigid filtration layer can sufficiently prevent shedding, so that one or both of the cover webs in the finished respirator will not be needed. Thus, the calendered rigid filtration web may enable removal of one reinforcement layer and one or both cover layers in the finished respirator, thereby removing one to three layers of conventional four layer constructions. This is particularly advantageous in that it can be removed.

The disclosed rigid filtration webs can be formed in a variety of different ways. For example, rigid filtration webs can be fabricated on and immediately adjacent to one or both major surfaces of a nonwoven web, similar to those shown in US Pat. Nos. 6,217,691 B1 and 6,358,592 B2 (both Bare et al.). It may comprise a transparent skin layer or layers formed by melting.

The finished respirator may optionally include an inner cover web of lightweight construction. The inner cover web can provide a smooth surface facing the wearer's face, thereby increasing respiratory comfort. If necessary, outer cover webs may also be used. As mentioned above, the inner or outer cover web, or both the inner and outer cover webs, are preferably unnecessary through the use of suitable calendered rigid filtration webs. The inner and outer cover webs can have any suitable configuration and composition. For example, the inner and outer cover webs can be spunbond webs or smooth BMF webs prepared as described in US Pat. No. 6,041,782 (Anggard Fat et al., '782). To improve reproducibility, the inner and outer cover webs preferably have the same polymer composition as the rigid filtration webs. The respirator can include one or more additional layers, other than those described above, if desired. For example, absorbent particles, such as the porous layer described in US patent application Ser. No. 11 / 431,152, filed May 8, 2006 and entitled " PARTICLE-CONTAINING FIBROUS WEB " One or more porous layers containing may be used to capture the vapor of interest.

During the formation of the disclosed rigid filtration webs, it will typically be useful to monitor web properties such as basis weight, web thickness, solidity, and Gurley stiffness. It may also be useful to monitor additional web properties such as EFD and Taber stiffness, or properties of the finished respirator such as pressure drop, initial% NaCl permeability,% DOP permeability, or quality factor (QF). . When exposed to 1 wt% sodium chloride aerosol flowing at 95 L / min, the finished respirator may have a maximum NaCl permeability of, for example, 20% or less. In another embodiment, the respirator has a pressure drop of less than 0.19 kPa (20 mm H ₂ O) or less than 0.09 kPa (10 mm H ₂ O) when exposed to 0.075 μm 2 weight percent sodium chloride aerosol flowing at 85 L / min. It may have a% maximum NaCl loading permeability of less than about 5% or less than about 1%.

Basis weight can be measured by gravimetric measurement using samples taken from several (eg, three or more) evenly spaced locations across the web in the width direction. Similar sampling can be used to measure web thickness. Solidity can be calculated from basis weight and web thickness measurements.

Gurley stiffness can be measured using Gurley Precision Instruments' model 4171E GURLEY ™ bending resistance tester. Rectangular samples (3.8 cm × 5.1 cm unless otherwise indicated) are die cut from the web with the long sides of the sample aligned in the web transverse (web cross) direction. The sample is loaded into the bending resistance tester with the long side of the sample in the web retention clamp. The sample is bent in both directions, ie with the test arm pressed against the first major sample face and then to the second major sample face, and the average of the two measurements is recorded as stiffness in milligrams. The test is treated as a fracture test and new samples are used if further measurements are needed.

EFD (unless otherwise specified), using the method described in Davies, CN, "The Separation of Airborne Dust and Particles", Institution of Mechanical Engineers, London, Proceedings 1B, 1952, (5.3 cm / sec. Can be measured using an air flow rate of 32 L / min.

Taber stiffness can be measured using a Model 150-B Taber ™ Stiffness Tester (commercially available from Taber Industries). A square section of 3.8 cm by 3.8 cm is carefully cut from the web using a sharp razor blade to prevent fiber fusion and its three and four samples and 15 ° sample deflection in its machine and transverse directions. Evaluated to measure stiffness.

Pressure drop, percent permeability, and filtration quality factor (QF) are measured using a challenge aerosol containing NaCl or DOP particles delivered at a flow rate of 95 or 85 L / min (unless otherwise indicated). It can be evaluated using a TSI ™ Model 8130 high speed automated filter tester (available from TSI Inc.). A MKS pressure transducer (commercially available from MKS Instruments) can be used to measure the pressure drop (ΔP, mm H ₂ O) through the filter. For NaCl testing at 95 L / min, particles can be produced from a 1% NaCl solution and the automated filter tester can be operated with both the heater and particle neutralizer turned on. For NaCl tests using particles of 0.075 μm diameter at 85 L / min, the particles were removed from a 2% NaCl solution to provide an aerosol containing the particles at an airborne concentration of about 16-23 mg / m 3. The automated filter tester can be operated with both the heater and the particle neutralizer turned on. For the DOP test, the aerosol may contain particles having a diameter of about 0.185 μm at a concentration of about 100 mg / m 3 and the automated filter tester may be operated with both the heater and the particle neutralizer turned off. Samples can be loaded at maximum NaCl or DOP particle transmission, and a calibrated photometer can be used at the filter inlet and outlet to measure particle concentration and% particle transmission through the filter. The equation

This can be used to calculate QF. Parameters that can be measured or calculated for the selected challenge aerosol include initial particle permeability, initial pressure drop, initial quality factor (QF), maximum particle permeability, pressure drop at maximum permeability, and milligrams of loaded particles at maximum permeability (maximum). Total weight challenge for the filter up to the transmission point). Initial quality factor (QF) values usually provide a reliable indicator of overall performance, where higher initial QF values indicate better filtration performance and lower initial QF values indicate reduced filtration performance.

The invention is further described in the following illustrative examples, where all parts and percentages are by weight unless otherwise indicated.

Example 1

Apparatus such as those shown in FIGS. 7 and 8 and in Wente, Van A. "superfine Thermoplastic Fiber", Industrial and Engineering Chemistry, vol. 48. 8, 1956, pp 1342-1346 and Naval Research Laboratory Report 111437, Apr. 15, 1954, using a procedure such as that described, meltblown monocomponent monolayer webs were formed from larger fibers and smaller size fibers of the same polymer composition. 1% polyone from PolyOne Corp. to assist in evaluating the distribution of 0.8% chimasorb 944 hindered amine light stabilizer and larger size fibers in the web as electret charging additives (POLYONE) No. CC10054018WE TOTAL 3960 polypropylene (melt flow polymer of 350) with the addition of the blue pigment was used to form larger size fibers. The resulting blue polymer blend was subjected to a Model 20 DAVIS STANDARD ™ 50.8 mm (2 inch) single screw extruder from the Davis Standard Division of Crompton & Knowles Corp. extruder). The extruder had a length of 152 cm (60 inches) and a length / diameter ratio of 30/1. Smaller size fibers were formed using EXXON PP3746 polypropylene (melt flow polymer of 1475) available from Exxon Mobil Corporation with 0.8% Kimmasov 944 hindered amine light stabilizer. This latter polymer was white and fed to a KILLION ™ 19 mm (0.75 inch) single screw extruder from Davis Standard Division of Cromton and Knowles Corporation. Using a 10 cc / rev ZENITH ™ melt pump from Zenith Pumps, 10 hole / cm (25 hole / inch) spacings in which alternating orifices are supplied by each die cavity The flow of each polymer was metered into a separate die cavity in a 50.8 cm (20 inch) wide orifice drilled using a 0.38 mm (0.015 inch) diameter orifice. Heated air lengthened the fibers at the die tip. The air knife used a positive set back of 0.25 mm (0.010 inch) and a 0.76 mm (0.030 inch) air gap. Appropriate vacuum was aspirated through the intermediate mesh collector screen at the web formation point, using a DCD (distance between die-collectors) of 57.2 cm (22.5 inches). By adjusting the polymer speed from each extruder, a web with 75% larger size fibers and 25% smaller size fibers was produced. Collector speed was adjusted as needed to provide a web with a basis weight of about 200 gsm. The extrusion temperature and the pressure of the heated air were adjusted as needed to provide a web with an EFD value of about 20 μm. The web was hydrocharged and dried with distilled water according to the technique taught in US Pat. No. 5,496,507 (Anggard Fatde et al., '507), then heated to 140 ° C. and had a gap of 0.76 mm and 3.05 m / min. Calendaring was performed between smooth steel rolls operated with. Table 1A below lists the job number, basis weight, EFD and Gurley stiffness for the calendared filtered web.

The calendered filtration web is combined with the instrument shown in FIGS. 1 and 2 in combination with a 17 gsm spunbond polypropylene inner cover web and 17 gsm spunbond polypropylene outer cover web in an apparatus such as that shown in FIG. 3. Made with the same flat fold respirator. The finished respirator was folded and unfolded, and was found to have both good storage characteristics when folded flat and a comfortable close fit when worn and a desirable unobtrusive shape. Initial NaCl particle permeability for the comparative four-layer flat fold respirator prepared using the respirator of the present invention and separate filtration and reinforcement layers was also evaluated. Table 1B below describes the job number, respirator type, initial pressure drop and initial NaCl permeability using a 0.075 μm diameter NaCl particle aerosol flowing at 85 L / min.

The data in Table 1B show that Task No. 1-1R respirator had lower initial pressure drop and lower initial NaCl permeability than the comparative four-layer respirator.

Example  2

Using the method of Example 1, meltblown monocomponent single layer webs were formed from larger fibers and smaller size fibers of the same polymer composition. Larger using exon PP3155 polypropylene (melt flow polymer of 36) available from Exxon Mobil Corporation with 0.8% Chimasov 944 hindered amine light stabilizer and 2% polyone number CC10054018WE blue pigment as electret charging additive A fiber of size was formed. The resulting blue polymer blend was fed to a Model 20 Davis Standard Extruder as used in Example 1. Smaller fibers were formed using Exxon PP3746 polypropylene with 0.8% Chimasov 944 hindered amine light stabilizer and 2% polyone number CC10054018WE blue pigment. This latter polymer was fed to a Cillian extruder as used in Example 1. By using a 13.5 inches (34.3 cm) DCD and adjusting the polymer speed from each extruder, a web with 65% larger size fibers and 35% smaller size fibers was created. Collector speed was adjusted as needed to provide a web having a basis weight of about 200 to about 250 gsm, and extrusion temperature and heated air pressure were adjusted as needed to provide a web having an EFD value of about 16 to about 18 μm. It was. The webs were hydrocharged with distilled water and allowed to dry according to the technique taught in the '507 patent of Anggard Fatde et al. The resulting web was made with a flat fold respirator such as the apparatus shown in FIGS. 1 and 2 and evaluated using a 0.075 μm diameter NaCl particle aerosol flowing at 85 L / min. Table 2A below lists the job number, basis weight, EFD, thickness and Gurley stiffness for calendared filtration webs, and initial pressure drop and initial NaCl permeability for the finished respirator.

The results in Table 2A show that each respirator will meet the European FFP1 filtering facepiece requirements (see EN149: 2001, Respiratory Protective Apparatus. Filtered half mask to protect against particles).

Example  3

Apparatus such as those shown in FIGS. 9 and 10 and in Wente, Van A. "superfine Thermoplastic Fiber", Industrial and Engineering Chemistry, vol. 48. 8, 1956, pp 1342-1346 and Naval Research Laboratory Report 111437, Apr. Using the same procedure as described in 15, 1954, four one-component single layer meltblown webs were formed from total 3960 polypropylene with 0.8% tristearyl melamine added as an electret charging additive. The polymer was fed to a Model 20 Davis Standard 50.8 mm (2 inch) single screw extruder with a length / diameter ratio of 20/1 and a compression ratio of 3/1. The Zenith 10 cc / rev melt pump is deformed by drilling the original 0.3 mm (0.012 inch) orifice every 9th orifice to 0.6 mm (0.025 inch), so that the number of smaller sized holes for larger sized holes The flow of polymer was metered into a meltblowing die drilled by a 10 inch wide orifice, providing a ratio of 9: 1 of the ratio and 60:40 of the larger pore size to the smaller pore size. The line of orifices had a hole spacing of 10 holes / cm (25 holes / inch). Heated air lengthened the fibers at the die tip. The air knife used a 0.25 mm (0.010 inch) amount of setback and 0.76 mm (0.030 inch) air gap. Missing or moderate vacuum was aspirated through the intermediate mesh collector screen at the web formation point. The polymer output rate from the extruder varied as needed from 0.36 kg / cm / hour (2.0 lb / inch / hour) at the time of initiation, the DCD varied from 11.50 inches to 29.21 cm (16.25 inches) and air The pressure was adjusted as needed to provide a web with basis weight and EFD as shown in Table 3A below. The webs were hydrocharged with distilled water and allowed to dry according to the technique taught in the '507 patent of Anggard Fatde et al. Table 3A below describes the sample number, basis weight, EFD, web thickness, initial pressure drop, initial NaCl permeability and quality factor (QF) for each web at a surface speed of 13.8 cm / sec.

The web was then slightly calendered by passing once or twice between the rolls heated to 141 ° C. and operating at a line speed of 3.05 m / min. A calendaring gap of about 1.5 to 2.2 mm was used. The calendering gap and web thickness for each sample are shown in Table 3B below.

Gurley stiffness values (measured using 25.4 x 38.1 mm samples) and pressure drop values (measured using a flow rate of 32 L / min) for each sample are shown in Table 3C below.

The results in Table 3C show that in particular the pressure drop was not significantly negatively affected by calendering. The web was made with a flat fold respirator such as the apparatus shown in FIGS. 1 and 2 and evaluated using a 0.075 μm diameter NaCl particle aerosol flowing at 85 L / min. Respirators made using non-calendering rigid filtration webs also used the inner and outer cover webs as used in Example 2 and had a three-layer configuration. A respirator made using a rigid filtration web calendared on one side also used the same inner cover web as the web used in Example 2 and had a two-layer configuration. A respirator made using a rigid filtration web calendered on two sides did not use a cover web and had a one layer configuration. Table 3D below lists the job number, percent transmission and quality factor (QF) for the finished respirator.

The results in Table 3D show that in particular the% transmittance and quality factor (QF) were not significantly negatively affected by calendaring.

Table 3E below shows the job number, initial pressure drop, initial% transmission, pressure drop at maximum transmission, maximum percent transmission, challenge at maximum transmission, and total aerosol challenge for a three-layer respirator made from non-calendering web samples. It is described.

The results in Table 3E show that a three-layered respirator manufactured using the non-calendering webs of Sample Nos. 3-1 to 3-4, 3-7 and 3-8 was used. It will be shown that it will pass the N95 NaCl loading test of Part 84.

Table 3F below shows the job number, initial pressure drop, initial% transmission, pressure drop at maximum transmission, challenge at maximum transmission, challenge for a two-layer respirator made from web samples calendared on one side, and Total aerosol challenge is described.

The results in Table 3F are shown in 42C.F.R. It will be shown that it will pass the N95 NaCl loading test of Part 84.

Table 3G below lists the job number, initial pressure drop, initial% transmission, pressure drop at maximum transmission, maximum percentage transmission, and challenge at maximum transmission for single layer respirators made from web samples calendered for both sides in Table 3G below. And total aerosol challenge is described.

The results in Table 3G show that a two-layered respirator manufactured using the webs of sample numbers 3-1 to 3-4, and 3-7 calendared for both sides was 42 C.F.R. It will be shown that it will pass the N95 NaCl loading test of Part 84.

Example  4

Using a device such as that shown in FIGS. 11-13, a FINA 3860 poly having a melt flow rate index of 70 is available from Total Petrochemicals for a one-component monolayer web (web 4-1). It was formed from propylene. The extrusion head 10 had 488 holes of 0.5 mm (0.020 inch) diameter arranged in a staggered 203 mm (8 inch) wide pattern. The polymer was fed to the extrusion head at 0.2 g / min per hole, where the polymer was heated to a temperature of 205 ° C. (401 ° F.). Two quench air streams (318b in FIG. 11; stream 318a not used) were 406 mm high with an approximate face velocity of 0.37 m / sec (73 ft / min) and a temperature of 1.7 ° C. (35 ° F.). As a top stream from a quench box at (16 inches) and as a bottom stream from a quench box at 197 mm (7.75 inches) in height to an approximate face velocity of 0.11 m / sec (22 ft / min) and ambient room temperature It was. 0.76 mm (0.030 inch) Air Knife Gap 30 (patent of Verrigan et al.), Air supplied to the air knife at a pressure of 14 psig (0.096 MPa); Three movable wall lengths, such as those shown in Verigan et al., Which use an inflator bottom gap width of 0.185 inches (mm) and a length of six inches (152 in.) Of the length of the thinner side (patent of Verigan et al.). Fire was used. The distance 317 (FIG. 11) from the extrusion head 310 to 31. FIG. 11 was 78.7 cm (31 inches), and the distance 321 (FIG. 11) from the elongator 316 to the collection belt 319. 68.6 cm (27 inches). The meltspun fiber stream was laminated on the collection belt 319 to a width of about 51 cm (about 20 inches). The collection belt 319 moved at a speed of about 1.8 m / min (6 ft / min). The vacuum under the collection belt 319 was estimated to be in the range of about 6 inches of H ₂ O to 12 inches of H ₂ O. The area 415 of the plate 411 had staggered 1.6 mm (0.062 inch) diameter openings leading to a 23% open area, and the web holding area 416 was staggered 1.6 leading to a 30% open area. It had openings of 0.062 inch diameter and the heating / bonding region 417 and the quenching region 418 had staggered 4.0 mm (0.156 inch) diameter openings leading to a 63% open area. Air is supplied through conduit 407 at a rate sufficient to provide about 14.2 m 3 / min (about 500 ft. ³ / min) of air in slot 409, 3.8 cm by 85.3 cm (1.5 inches by 26 inches). It was. The bottom of the plate 408 was 3.175 cm (1.25 inches) from the collected web 320 on the collector 319. The temperature of the air passing through the slot 409 of the quench flow heater was 157 ° C. (315 ° F.) as measured at the point of entry of the heated air into the housing 401.

The webs outside the quench zone 420 are self-supporting and joined to have sufficient integrity to be handled using conventional processes and equipment, and the webs can be wound or molded by conventional winding into a storage roll. Various operations may be performed, such as heating and compressing the web over a hemispherical mold to form a respirator. The webs were hydrocharged with distilled water and allowed to dry according to the technique taught in the '507 patent of Anggard Fatde et al.

A second one-component monolayer web (web 4-2) was similarly prepared from Pina 3860 polypropylene with 0.5% by weight of the Chimasov 944 hindered amine light stabilizer from Ciba Specialty Chemicals. The condition is that the extrusion head 10 is arranged in a pattern of 10 cm by 20 cm (4 inches by 8 inches) with a hole spacing of 0.64 cm (0.25 inches) and the 512 long lengths of the pattern are arranged across the web. Same as web 4-1, except it had a hole. The upper quench stream had an approximate face velocity of 0.32 m / sec (63 ft / min). The elongator bottom gap width was 4.8 mm (0.19 inch). The meltspun fiber stream was laminated onto the collection belt 319 to a width of about 46 cm (about 18 inches). The collection belt 319 moved at a speed of about 1.77 m / min (5.8 ft / min). The bottom of the plate 408 was 4.1 inches (1.6 inches) from the collected web 320 on the collector 319. The collected webs were hydrocharged with distilled water and allowed to dry according to techniques taught in Russo et al.

Charged webs were evaluated to determine the flat web properties shown in Table 4A below.

The web was made with a flat fold respirator such as the apparatus shown in FIGS. 1 and 2 and evaluated using a 0.075 μm diameter NaCl particle aerosol flowing at 85 L / min. The results are shown in Table 4B below.

Many embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims (35)

At least one rigid filtration panel coupled to the remainder of the respirator through at least one dividing line, the panel comprising a porous monocomponent monolayer nonwoven web, the web being charged and mixed continuous 1 of the same polymer composition. Flat-folded personal, comprising component polymer fibers and having a sufficient basis weight or interfiber bonds such that the web exhibits Gurley Stiffness greater than 200 mg and the respiratory tract exhibits a pressure drop less than 20 mm H ₂ O. Respiratory system. The respirator of claim 1, wherein the nonwoven web comprises a bimodal mass fraction / fiber size mixture of mixed continuous monocomponent polymeric microfibers and larger size fibers. The respirator of claim 1, wherein the nonwoven web comprises oriented meltspun fibers that are partially crystalline and partially amorphous. The respirator of claim 1, wherein the nonwoven web has a basis weight of about 100 to about 500 gsm. The respirator of claim 1, wherein the nonwoven web has a basis weight of about 150 to about 250 gsm. The respirator of claim 1, wherein the nonwoven web is calendered. The respirator of claim 1, wherein the nonwoven web has a Gurley stiffness of at least about 300 mg. The respirator of claim 1, further comprising an inner cover web. The respirator of claim 8, wherein the inner cover web and the rigid filtration panel have the same polymer composition. The respirator of claim 1, wherein the polymer is polypropylene. The respirator of claim 1, wherein the polymer is poly-4-methyl-1 pentene. The respirator of claim 1, wherein the respirator exhibits a maximum transmission of 20% or less when exposed to 1 wt% sodium chloride aerosol flowing at 95 L / min. The respirator of claim 1, exhibiting a maximum loading transmission of less than 5% when exposed to 0.075 μm 2% sodium chloride aerosol flowing at 85 L / min. The respirator of claim 1, wherein the respirator exhibits a maximum loading transmission of less than 1% when exposed to 0.075 μm 2% sodium chloride aerosol flowing at 85 L / min. The method of claim 1, First portion; A second portion that is distinguished from the first portion by the first dividing line; A third portion, distinguished from the second portion by the second dividing line; And When viewed from the front in an oriented state such as when the respirator is used on a wearer, the non-wrinkle body includes a bisecting fold that is substantially vertical and includes a bifold fold extending through the first, second and third portions; , The first, second and third portions are respectively divided into left and right panels comprising a rigid filtration panel, wherein the respirator can be folded into a substantially flat folded shape along a bistable fold. The respirator of claim 15, further comprising an inner cover web having the same polymer composition as the rigid filtration panel. The method of claim 1, A filtration structure comprising an optional inner cover web, a web comprising a charged microfiber, and an optional outer cover web, wherein the optional inner cover web and the optional outer cover web each comprise a filtration layer. Disposed on opposite first and second sides of, The filtration structure is divided into upper, middle and lower filtration panels, the central panel being separated from the upper and lower panels by the first and second dividing lines, At least the central panel includes a rigid filtration panel, wherein the respirator can be folded into a shape that is folded substantially flat along the first and second dividing lines. The respirator of claim 17, wherein the inner cover web has the same polymer composition as the rigid filtration panel. The respirator of claim 17, wherein at least one of the first or second dividing lines is curved. The filter body of claim 1, comprising a filtration body comprising an optional inner cover web, a filtration layer comprising a web comprising charged microfibers, and an optional outer cover web, the filtration body comprising a first portion and a second portion. Having a central portion therebetween, the central portion comprising a rigid filtration layer and defined by the first and second dividing lines and having a width of about 160 to 220 mm and a height of about 30 to 110 mm, wherein the respirator is Can be folded flat for storage with at least partially facing the surface of the central portion and the second portion in contact with the surface of the first portion, the respirator being cup-shaped on the wearer's nose and mouth when unfolded for use. A respirator that forms an air chamber that does not cover the face. a) obtaining a monocomponent monolayer nonwoven web comprising charged and mixed continuous monocomponent polymer fibers of the same polymer composition and having sufficient basis weight or interfiber bonds to exhibit a Gurley stiffness of greater than 200 mg; b) forming at least one divider in the charged web to provide at least one panel at least partially defined by the divider; And c) flattening the web to provide a mask body that exhibits a pressure drop less than 20 mm H ₂ O and that can be folded into a substantially flat folded shape and unfolded into a convexly open shape. Method for manufacturing a fold type personal respirator. The method of claim 21, further comprising reclaiming the waste portion to recover the trimmed waste portion from the web to produce additional rigid filtration webs. The method of claim 22, wherein the polymer and the waste portion consist essentially of polypropylene and optional electret charging additives. 22. The method of claim 21 comprising forming the nonwoven web as a bimodal mass fraction / fiber size mixture of mixed continuous monocomponent polymeric microfibers and larger size fibers. 22. The method of claim 21 including forming a nonwoven web from partially crystalline and partially amorphous oriented meltspun fibers. 22. The method of claim 21 comprising forming a nonwoven web in a basis weight of about 100 to about 500 gsm. The method of claim 21 comprising forming the nonwoven web in a basis weight of about 150 to about 250 gsm. The method of claim 21 comprising calendering the nonwoven web. The method of claim 21 comprising forming a nonwoven web to have a Gurley stiffness of at least about 300 mg. 22. The method of claim 21, further comprising forming a preform comprising an inner cover web. The method of claim 30, wherein the inner cover web and the rigid filtration panel have the same polymer composition. The method of claim 31, wherein the polymer is polypropylene. The method of claim 31, wherein the polymer is poly-4-methyl-1 pentene. 22. The predetermined first and second angles to the bisectoral fold line of claim 21, wherein the web is folded about a bisector axis to produce a folded preform having a bisectoral fold line and the folded preform affects the size of the respirator. The method further comprises the step of welding, sewing or otherwise fastening. a) forming a monocomponent monolayer nonwoven web of mixed continuous monocomponent polymer fibers of the same polymer composition and charging the web, wherein the web has a sufficient basis weight or interfiber bond to exhibit a Gurley stiffness of greater than 200 mg Has-; b) forming at least one divider in the charged web to provide at least one panel at least partially defined by the divider; And c) flattening the web to provide a mask body that exhibits a pressure drop less than 20 mm H ₂ O and that can be folded into a substantially flat folded shape and unfolded into a convexly open shape. Method for manufacturing a fold type personal respirator.

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